FSP1 is a protein identified as a marker specific to fibroblast (non-patent document 1), and encodes a filament-bound S100A4 protein having an EF hand binding domain (non-patent document 2). The present inventors found that promoted expression of FSP1 is seen in podocytes and crescent cells in active glomerular diseases such as crescentic glomerulonephritis and the like (non-patent document 3), and urinary FSP1 of crescentic glomerulonephritis patients can be a biomarker of the diseases (non-patent document 4). Furthermore, they also found that urinary FSP1 can be a disease activity index since it shows a positive correlation with the frequency of appearance of glomerulus that forms a cellular crescent.
However, the correlation between FSP1 in a biological sample and renal disease has been verified only for crescentic glomerulonephritis, and there is no report yet on the relation between renal interstitial disease and FSP1 in a biological sample. In addition, a method of conveniently determining a lesion site in nephritis patients has still been demanded in clinical situations.